The manufacture of components for internal combustion engines is an extremely mature technology which has developed steadily for a period approaching an entire century. The science and technology of manufacturing engine components to meet the ever increasing demands for quality and reduced costs have driven manufacturers toward ever higher levels of automation and mechanization. The enormous costs associated with such high tech equipment, however, demands that production engineers employ standard equipment components whenever possible, thereby necessitating innovation of only the minimum amount of specialized tooling to cause such standard components to operate efficiently.
One area where the demand for minimizing costs while achieving the very highest possible quality is in the manufacture of flywheel assemblies for internal combustion engines. Such assemblies are essential to the proper functioning of an internal combustion engine in order to assure the smoothing out of torque impulses caused by the separate combustion strokes of each piston of the engine. Thus, designers are required to carefully consider the necessary weight and shape of the flywheel in association with the requirements of the engine in order to assure that the primary function of the flywheel is properly performed. Furthermore, the flywheel is often required to perform auxiliary functions such as, for example, providing a hub for mounting a ring gear adapted to engage the drive gear of a starter motor. The flywheel is also often used to provide the mounting of a clutch element to thereby provide a path for engine torque to be passed to the input of a vehicle transmission upon engagement of the corresponding clutch. Achievement of all of these functions requires that the flywheel be very carefully manufactured to close tolerances and to be assembled thereafter with a ring gear and clutch element.
To provide the necessary primary function of smoothing the torque impulses of the individual engine pistons, the flywheel for many engines must be quite large and heavy, (i.e., up to 20 inches or more in diameter and 300 lbs. or more in weight) making difficult the process of casting, handling and machining to achieve the desired final product. Because of the large rotational momentum desired from a flywheel assembly, and due to the rather large diameter and weight necessitated thereby, it is vitally important that the flywheel assembly be balanced very carefully prior to installation on a internal combustion engine. In one known process for achieving an acceptable flywheel assembly, it has been known to cast the flywheel hub and to move the hub through a series of work stations arranged to allow for careful machining by numerically controlled machine tools of the various critical surfaces of the flywheel, including the machining of a ring gear mounting surface. The flywheel hub is then balanced at a work station designed for this purpose and the ring gear is heat shrunk onto the ring gear mounting surface.
While the prior art approach is satisfactory in many ways, it failed to achieve all of the objectives associated with a relatively flawless, properly balanced flywheel assembly at a speed of production and at a cost adequate to meet modern competitive demands.
Prior art techniques for heat shrinking ring gears onto a flywheel hub are known as illustrated in U.S. Pat. No. 3,775,831. However, the precise machining steps involved in the procedure for forming the flywheel hub is not shown. Moreover, the conveying and handling mechanism illustrated in this patent fails to solve the numerous problems associated with achieving a high quality, low cost and properly balanced flywheel assembly.
Still other techniques for heat shrinking gears onto a hub support are known such as disclosed in an article in American Machinists. Jun. 19, 1948, entitled: "Calculations Improve Shrink Fits Large Gears and Wheels", pages 142-145. Again, however, techniques necessary for achieving a high production flywheel assembly are not disclosed in this article.
Outside of the flywheel manufacturing art, it is known in assembly processes generally to shrink fit a component followed by additional machining steps to assure that any misalignment, within limits, may be compensated for in the subsequent machining as taught by U.S. Pat. No. 3,852,872 to Afanador et al.
Yet another prior art technique is disclosed in U.S. Pat. No. 2,647,847 to Black et al for interfitting machine parts wherein one component is heat shrunk onto another followed by subsequent machining operations to insure uniform bore. Still the prior art has failed to solve the problems associated with achieving the maximum degree of quality in forming a flywheel assembly while also assuring high production rates utilizing the minimum degree of investment in the tooling necessary for carrying out the desired end results.